This invention relates to fluoran derivatives as new compounds useful as colorless chromogenic materials and a new recording system utilizing the same.
There are known various kinds of recording systems utilizing the colorforming reaction between a colorless chromogenic material and an electron accepting acidic reactant material by the medium of mechanical, heat, electric or light energy. Among them there are included a pressure-sensitive record sheet, a heat-sensitive record sheet, an electrothermal record sheet, an ultrasonic record sheet, an electron beam record sheet, an electrostatic record sheet and a photosensitive record sheet. The colorless chromogenic materials of these kinds also find their usefulness in photosensitive printing compositions, typewriter ribbons, ball-point pen ink, crayon and stamp ink.
In the recording system utilizing the color forming reaction between a colorless chromogenic material (hereinafter referred to as "color former") and an electron accepting acidic reactant material (hereinafter referred to as "acceptor"), images of various colors can be developed by using different kinds of color formers. There is now an increased demand for record materials which develop black color images which can be reproducible for copies. Theoretically, images of substantially black color can be obtained by using a mixture of various color formers which develop the respective different colors, e.g., red, blue, yellow and green. The utilization of a mixture of different color formers for obtaining a black color has, however, a disadvantage that the once developed black color images cannot be maintained for a long time because different color formers have different color developing speeds and different light and moisture resistances. Some attempts have been made to obtain images of substantially black color through the utilization of a single color former. However, there has yet been found no single color former which can develop substantially black color images without sacrificing all the stability of the color former before color developing, color developing speed, color density, color tone and stability of the color images developed and its production cost.
The primary object of the invention is to provide novel fluoran derivatives useful as color formers for use in various recording systems.
Another object of the invention is to provide novel color formers for use in recording systems in which the color images when developed therefrom assume a substantially deep-black color and have a good light resistance.
A further object of the invention is to provide novel color formers for use in heat sensitive recording systems in which substantially no fogging occurs on the record materials to which they are applied.
A still further object of the invention is to provide novel color formers for use in recording systems which have a good and instant color developability.
It is also included among the objects of the invention to provide an improved recording system in which a fluoran derivative as a new compound is used as a color former and the color images when developed therefrom have a good light resistance and assume a substantially deep-black color which is suitable for reproduction of copies.
Other objects and advantages of the invention will become apparent from the following description.